The standard of care for the diagnosis of many epithelial precancerous and early cancer conditions is visual inspection of the patient directly or through an endoscope/laparoscope to identify abnormal tissue. Biopsies can then be obtained from these locations, processed, cut and stained with Hematoxylin and Eosin (H&E), and then observed under a microscope by a pathologist. A pathologist can view the slide at progressively increasing resolutions and renders a diagnosis by comparing its architectural and cellular patterns with his/her knowledge of patterns associated with different disease states.
For a number of cases, however, metaplasia, dysplasia, and early cancer may not be visually identified. In these situations, the only available option may be to obtain biopsies at random locations which are routinely conducted in the colon, esophagus, prostate, and bladder, among others. When the disease is focal or heterogeneously distributed within a much larger suspect area, a random biopsy procedure may be analogous to “finding a needle in a haystack,” resulting in poor diagnostic yields and uncertain patient management.
Since random biopsies may only facilitate the assessment of less than 0.1% of the potentially involved tissue, these procedures are usually fraught with significant sampling error and diagnostic uncertainty. Other tasks, such as the delineation of surgical tumor margins, can also be affected by this difficulty, resulting in all too frequent re-excisions or time-consuming frozen section analysis. Thus, there may be a need for providing an apparatus and a method for guiding biopsy that is superior to visual inspection and that can direct the physician to a location that is more likely to harbor the most severe disease.
Barrett's esophagus is a condition of the tubular esophagus, where the squamous epithelium changes to intestinal epithelium, termed specialized intestinal metaplasia (SIM). Thought to be precipitated by severe or longstanding gastroesophageal reflux disease (GERD), BE can undergo dysplastic progression, leading to esophageal adenocarcinoma. Current management of Barrett's esophagus can include endoscopic surveillance at regular time intervals, consisting of upper endoscopy with 4-quadrant random biopsy, to identify dysplasia or adenocarcinoma at an early stage. This method suffers from a low sensitivity, as it is compromised by the poor ability of endoscopists to identify SIM/dysplasia and the low fractional area of tissue sampled by biopsy.
In the past, in the field of biomedical optics, imaging methods have been developed to provide improved tissue diagnosis in vivo. These imaging methods can be generally categorized as macroscopic or microscopic techniques.
Macroscopic, e.g., wide field imaging methods including autofluorescence, fluorescence lifetime imaging, ALA-fluorescence, reflectance and absorption spectroscopic imaging, narrow-band imaging, and chromoendoscopy. These macroscopic methods can be used to quickly evaluate large regions of tissue. While many of these techniques are promising, the information provided is often quite different from that conventionally used in medicine for diagnosis.
Microscopic imaging, at times referred to as “optical biopsy,” is another approach that enables the visualization of tissues at a resolution scale that is more familiar to physicians and pathologists. In the past, the minimally-invasive endoscopic microscopy techniques that have been developed to visualize the architectural and cellular morphology required for histopathologic diagnosis in vivo facilitate a very small field of view, however, and the probes are usually manually manipulated to obtain images from discrete sites (“point-sampling”). As a result, such techniques suffer from substantially the same sampling limitations as excisional biopsy, and may not be well suited for guiding biopsy.
One such microscopic imaging technique, reflectance confocal microscopy (RCM), can be suited for non-invasive microscopy in patients as it offers imaging of cellular structures at ˜1 μm resolution, can measure microstructure without tissue contact, and does not require the administration of unapproved exogenous contrast agents.
RCM can reject or ignore multiply scattered light from tissue, and detects the singly backscattered photons that contain structural information by employing confocal selection of light reflected from a tightly focused beam. Most commonly, RCM can be implemented by rapidly scanning a focused beam in a plane parallel to the tissue surface, resulting in transverse or en face images of tissue. A large numerical aperture (NA) of RCM can yield a very high spatial resolution. Sensitive to the aberrations that arise as light propagates through inhomogeneous tissue; high-resolution imaging with RCM can typically be limited to a depth of 100-200 μm, which is sufficient for most epithelial disorders that manifest near a luminal surface.
While RCM has been demonstrated in the skin, the development of endoscopic confocal microscopy systems has taken longer due to technical challenges associated with miniaturizing a scanning microscope. One difficulty with such technique is providing a mechanism for rapidly raster-scanning the focused beam at the distal end of a small-diameter, flexible probe. A variety of approaches have been attempted to address this problem, including the use of distal micro electro mechanical systems (MEMS) beam scanning devices, and proximal scanning of single-mode fiber bundles.
Another challenge can be the miniaturization of high NA objectives used for optical sectioning. Possible solutions employing a gradient-index lens system, dual-axis objectives or custom designs of miniature objectives have been described. First, demonstrations of these technologies in patients are beginning to appear; detailed images of the morphology of cervical epithelium have been obtained in vivo using a fiber optic bundle coupled to a miniature objective lens and fluorescence based images of colorectal and esophageal lesions were shown using commercial instruments.
Even though endoscopic RCM has been demonstrated in patients, this technique is likely not currently optimized for biopsy guidance. One reason can be that such technique provides microscopic images only at discrete locations, the so-called “point sampling” approach problem mentioned above. Point sampling is inherent to RCM since it has an extremely limited field of view (e.g., 200-500 μm), which is less than that of an excisional biopsy. As a result, endoscopic RCM may likely have the same sampling errors and diagnostic yield limitations as excisional biopsy.
In order to use endoscopic RCM for biopsy guidance, the imaging paradigm may be shifted away from point sampling to microscopy with extremely large fields of view where every possible location within the tissue of interest is sampled. The output of this paradigm, which can be termed “Comprehensive Volumetric Microscopy (CVM),” can include microscopic images of entire organ or luminal surfaces in three-dimensions.
For CVM, imaging speeds of current techniques may need to be increased by at least an order of magnitude above video rate, due to the very high bandwidth of the microscopic information and the constraint of obtaining such data in a realistic procedural time (e.g., <20 min). In addition, catheter/endoscope technology can be developed to automatically scan the microscope over these large tissue surface areas rapidly and with a high degree of precision.
Recently, CVM has been implemented using a second-generation form of optical coherence tomography (OCT), called optical frequency domain imaging (OFDI), and rapid helically scanning catheters. This research has facilitated the acquisition of three-dimensional microscopic images of the entire distal esophagus in a few minutes and long segments of coronary arteries in patients in less than 5 seconds. (See Suter M. J. et al., “Comprehensive microscopy of the esophagus in human patients with optical frequency domain imaging”, Gastrointestinal endoscopy, 2008, Vol. 68(4), pp. 745-53; and Tearney G. J. et al., “Three-dimensional coronary artery microscopy by intracoronary optical frequency domain imaging: First-in-human experience”, Journal of the American College of Cardiology, Imaging, 2008, pp. 1:752-61
While OFDI shows significant potential for certain clinical applications, its ˜10 μm resolution may not necessarily be sufficient for dysplasia and early cancer diagnosis, which can require knowledge of tissue morphology at both architectural and cellular levels. Thus, there may be a need to provide a new exemplary variant of RCM that is capable of rapidly obtaining high-resolution comprehensive volumetric images through an endoscopic probe.
One approach is to use spectrally encoded microscopy (“SECM”) technique(s). SECM's rapid imaging rate and its fiber-optic design can enable comprehensive volumetric RCM through an endoscopic probe. An SECM probe has been described which can scan an area equivalent to that of the distal esophagus (about 5.0 cm length, and about 2.5 cm diameter), at a single depth location, in approximately 1 minute. (See, e.g., Yelin D. et al., “Large area confocal microscopy”, Optics Letters, 2007; 32(9):1102-4).
Spectrally encoded confocal microscopy (“SECM”) is a single fiber-optic confocal microscopy imaging procedure, which uses a broad bandwidth light source and encodes one dimension of spatial information in the optical spectrum (as illustrated in the example of FIG. 1). As shown in FIG. 1, at the distal end of the probe, the output from the core of a single-mode or dual-clad fiber 110 is collimated by a collimation lens 115 and illuminates a transmission diffraction grating 120. An objective lens 130 focuses each diffracted wavelength to a distinct spatial location 141, 142, or 143 within the specimen, producing a transverse line focus 150 where each point on the line has a different wavelength or color. After reflection from the tissue, the light passes back through the lens 130, is recombined by the grating 120, and collected by the fiber 110. The aperture of the fiber 110 provides the spatial filtering mechanism to reject out-of-focus light. Outside the probe (within the system console) the spectrum of the returned light is measured and converted into confocal reflectance as a function of transverse displacement within the sample. Spectral decoding of this line in the image can be performed very rapidly, e.g., at rates of about 70 kHz, which can be approximately 10 times that of video rate confocal microscopy systems and up to about 100 times faster than some endoscopic RCM systems. The other transverse axes of the image can be obtained by relatively slow and straightforward mechanical actuation that may regularly employ for a wide variety of endoscopic probes. Images obtained by SECM demonstrate its capability to image subcellular-level microstructure relevant to the diagnosis of dysplasia and cancer (see FIG. 2). FIGS. 2A and 2B show exemplary SECM images of swine duodenum, obtained ex vivo, after compression of the bowel wall, showing the architecture of the duodenal villi and nuclear detail. Illustrated imaging depths are 50 μm and 100 μm shown in FIGS. 2A and 2B, respectively.
Accordingly, there may be a need to overcome at least some of the above-described issues and/or deficiencies.